In general, a dialysis machine is used as a substitute for the natural kidney functions of a human body. As such, the dialysis machine cleanses the blood of the natural accumulation of bodily wastes and separates the wastes from the blood outside of or extracorporeally of the body. The separated wastes are discharged, and the cleansed blood is returned to the body.
The wastes are separated from the blood in a dialyzer. The dialyzer includes an internal housing which is separated by a porous medium into a blood side or compartment and a dialysate side or compartment. The blood removed from the patient flows through the blood side of the dialyzer. A prepared solution of dialysate is passed through the dialysate side of the dialyzer. The wastes from the blood pass through the medium by osmosis, ionic transfer or fluid transport into the dialysate and, depending upon the type of dialysis treatment, desirable components from the dialysate may pass in the opposite direction through the medium and into the blood. The transfer of the wastes into the dialysate cleanses the blood while allowing the desired components from the dialysate to enter the bloodstream.
As is apparent, the dialysis machine must be properly operated to perform effective dialysis in a safe and reliable manner. With the blood of the patient being removed and handled outside of the patient's body in an extracorporeal flow path, care must be taken that the treatment progresses safely and as intended according to the dialysis prescription for the patient. Since the patient's blood and the dialysate separated only by the dialyzer medium, it is apparent that numerous safety concerns must be satisfied on a continual and reliable basis.
Because of the potential for extremely serious consequences resulting from a failure or other unsafe condition, modern dialysis machines incorporate a large number of safety features as well as extensive control system features. The safety features include sensors located in the extracorporeal and dialysate flow paths to derive signals representative of the operating conditions or parameters which indicate the proper operation of the dialysis machine and/or the early development of a safety or risk condition. The control system features result in operational control over the pumas, dialysate heater, flow control valves and other devices associated with the extracorporeal and dialysate flow paths.
Because of the pre-eminent importance of the safety system, all known modern dialysis machines utilize microcontrollers or similar types of processor devices to execute the safety functions. Generally speaking, modern microcontrollers offer a greater possibility of more effective control over the safety features than other types of safety systems. Typically one microcontroller is used to execute the safety functions, and at least one and frequently two other microcontrollers execute the control system functions. Upon recognizing a safety or risk condition, the safety microcontroller takes control of the dialysis machine and places it in a safe state which prevents or greatly reduces the risk of injury to the patient.
In large measure, the use of separate microcontrollers for the safety and control systems is a result of the relatively stringent standards established by governmental, health and safety groups pertaining to dialysis machines. The multiple-microcontroller approach to achieving the basic safety and control system functions satisfies the regulatory standards by making the functionality of the safety system microcontroller independent of and separate from the functionality of the control system microcontroller.
The safety standards also apply to the entry of the information when setting up the machine to perform the dialysis treatment, as well as to the entry of information during the progress of the treatment. In general, the safety standards are concerned with promoting operator accuracy when entering information, and assuring that the entered information is not corrupted before it is used by the control system and safety system microcontrollers.
Since in some cases the machine can not protect against an operator-generated human error, many dialysis machines require the operator to enter information twice before the microcontrollers will accept the information. The theory behind the double-entry requirement is that the operator is more likely to recognize an error if the operator is required to check, view or consider the entered information twice. Generally the first entry results in the information being recorded in memory and then displayed to the operator. After the operator has again entered the same information, the microcontroller compares the first and second entries. If the two entries are the same, the first entry previously recorded in memory will be transferred to the control system and safety system microcontrollers for use during the treatment. Other typical information entry techniques used in dialysis machines display the second entry in a separate location from the display of the first entry. The operator must then mentally compare the two entered values, and if they are equal, accept the entered value. In this double-display technique, the dialysis machine does not make the comparison, but instead leaves the comparison to the operator.
While the double-entry and double-display techniques have generally proved successful, they are somewhat tedious, repetitious and time-consuming for the operator. The typical machine setup procedure requires the entry of a significant number of different values, and the time associated with the double-entry detracts from the other activities required to ready the machine for treatment. Furthermore, the repetitiveness of the entries can lead to a type of monotony which may cause the operator to be less vigilant in visually comparing the two displayed values, or which results in a certain level of tension and tedium resulting from making the second entry, or which results in frustration when the operator encounters difficulty in correctly entering the information in sequential entries.
These and other considerations have contributed to the evolution of the present invention which is summarized below.